Recently, attention has been directed to the direct smelting process wherein an ore or metal oxide is reduced in a molten state or thermally decomposed with use of a thermal plasma produced by arc discharge to directly obtain a metal or a product enriched in metal.
The direct smelting process attracts attention because of its advantages. When the thermal plasma is used for smelting, a superhigh temperature is obtained which can be maintained with good stability, giving rise to a reaction which requires such a high temperature as is not available with usual heat sources. Since the reaction velocity increases exponentially with temperature, the reaction can be carried out within a shorter period of time with use of an apparatus of smaller size.
As disclosed in U.S. Pat. No. 3,856,918 and Examined Japanese Patent Publication SHO 60-53088, the direct smelting process is practiced by causing arc discharge across a cathode and an anode, and feeding a powder of ore or the like along with a plasma forming gas to melt and decompose the powder while it is passing through a plasma arc, or feeding the powder around a plasma arc to melt and decompose the powder by the radiant heat of the arc. To produce a reducing gas in this process, hydrogen, methane, carbon monoxide or like reducing gas is used as the plasma forming gas along with an inert gas. As disclosed in Examined Japanese Patent Publication SHO 53-44128, it is also known to coat the particles of the powder with a layer of carbonaceous substance in order to effect accelerated reduction.
With the above techniques, however, it is impossible to retain the particulate ore or the like in or around the plasma arc for a sufficient period of time, making it difficult to reduce the material in a molten state or decompose the material and therefore necessitating a cumbersome pretreatment such as the adjustment of the size of particles or coating of the particulate material with a carbonaceous substance.
Further to produce a stabilized plasma arc for a reducing reaction, the process requires a large quantity of hydrogen,argon, methane or like gas as the plasma forming gas.
Additionally, the plasma generator requires means for cooling the electrodes and means for feeding the plasma forming gas and the particulate material. These means render the apparatus complex and result in an increased smelting cost along with the use of large quantity of the plasma forming gas.
An object of the present invention, which has been accomplished in view of these problems, is to provide a direct smelting process which can be practiced easily by simple equipment regardless of the form of material to be smelted and without using any plasma forming gas.